archiecobbs opened a new issue, #370:
URL: https://github.com/apache/mina-sshd/issues/370
### Version
sshd-2.9.2-55-gd4b951a10
### Bug description
`ModifiableFileWatcher` is supposed to detect when a file changes.
However, it's possible for a file to change and for `ModifiableFileWatcher`
to not detect the change.
Consider the following somewhat contrived but not unreasonable scenario:
* User public key files are built into an RPM and stored in files
`/opt/pubkey/adam`, `/opt/pubkey/jeff`, etc.
* The current admin's key (e.g., Adam's) is stored as a symlink like
`/var/pubkey/admin -> /opt/pubkey/adam`
* We authorization SSH login via `new AuthorizedKeysAuthenticator(new
File("/var/pubkey/admin").toPath())`
Adam gets fired for being an evil hacker, so we quickly make Jeff the new
admin like this:
```bash
$ ln -sf /opt/pubkey/jeff /opt/pubkey/adam
```
Phew! We think Adam is no longer authorized, but...
* `/var/pubkey/admin` has never not existed at any point in time
* `/opt/pubkey/adam` and `/opt/pubkey/jeff` are the exact same size since
they contain the same type of public key and the usernames (added as a comment
after the public key) are the same length
* `/opt/pubkey/adam` and `/opt/pubkey/jeff` have the same modification
timestamp, since they were installed at the same time as part of the same RPM
Therefore, `ModifiableFileWatcher` will fail to notice that the file has
changed. So evil Adam is still the admin!
Solution: Along with `lastExisted`, `lastModifed`, and `lastSize`,
`ModifiableFileWatcher` should also track the value of
`BasicFileAttributes.fileKey()` in a field `lastFileKey`, and detect a file
change if this value changes.
### Actual behavior
No file change detected.
### Expected behavior
File change detected.
### Relevant log output
_No response_
### Other information
_No response_
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